New observations verify the theory about the process of the formation of the planets
Avishai Gal-Yam
Until recently, astronomers could only observe our solar system. The space of the theory that explains the formation of the planets was therefore built in order to explain what is happening in this system. In recent years, following a series of technological breakthroughs in the production and operation of sophisticated telescopes, astronomers are able for the first time to observe systems of planets that are in the process of formation around other suns: infrared radiation observations, for example, show how stars in the initial formation processes emerge from clouds of gas and dust.
As a result of the technological breakthroughs, much research effort has recently been devoted to examining the processes of star formation. The researchers are trying to find out, without success yet, why the stars that are formed are different from each other: there are giant stars whose mass is tens of times greater than that of the Sun and in contrast dwarfs whose mass is only about a tenth of that of the Sun. Another question that astronomers are trying to find an answer to is why most stars are not formed singly but as pairs: two stars orbiting each other.
Stars form from clouds of gas, mainly hydrogen, floating in interstellar space. The force of gravity acting between the gas particles causes the clouds to contract so that the distance between the gas particles is small. As a result, the attraction between them increases. This process is called "gravitational collapse". The gas clouds are shrinking, the gas has become more compressed and hotter. The temperatures in the heart of the gas clouds collapsing under the influence of gravity can reach up to millions of degrees Celsius: in such cases the collisions between the gas particles are enormously powerful.
Sometimes, atoms of hydrogen gas collide with each other with such great force that they become atoms of another element: helium gas. This process is called nuclear fusion (or fusion) - the process on which the hydrogen bomb is based. When such a process occurs in the heart of a gas cloud, a huge amount of energy is released in the form of heat and radiation: it can be compared to the explosion of millions of hydrogen bombs at the same time. The energy released in the core of the cloud as a result of the nuclear fusion process pushes the outer layers of the cloud outward and balances the force of gravity pulling them inward: the gas cloud, which is now very hot, reaches a state of equilibrium. The heat and radiation, which originate in the center of the cloud, are emitted from the outer layers, and the gas cloud turns into a hot ball of gas that emits radiation and heat - and this is a star.
The described process explains how the stars are formed - our sun, for example. But how were the planets formed? The nature of the planets is fundamentally different from that of the stars of the Sabbath. One of the big differences between them is that the stars of the Sabbath emit their own light. They are visible They are so pale to us only because they are an enormous distance away from us. In contrast, the planets are much smaller bodies. They are not sources of light in themselves: the light that reaches our eyes from them is sunlight reflected off their surfaces.
The accepted scientific assumption is that the planets are formed from the remnants of the gas cloud from which the main star of the system was formed. The remnants that remain surround the young star and form a disk. As mentioned, most of this material is hydrogen gas, but it also contains heavier elements: carbon, oxygen, nitrogen and iron. In the resulting disk, these materials crystallize into tiny dust grains, which coalesce and become larger clumps of material. These clumps collide with each other and form bodies that are similar in shape to asteroids in our solar system. Over time, the largest clumps, with the help of gravity, capture all the matter moving close to their orbit and become planets, such as Earth, Venus and Mars. These planets consist mainly of oxygen, carbon, nitrogen and iron and are called Earth-like planets. Especially heavy planets, which are in a distant orbit from the planet Saturn, for example Jupiter and Saturn in our solar system, have a strong enough gravitational force to capture a shell of hydrogen gas: these stars are called "gas giants".
Two groups of astronomers from the USA recently used the "Hubble" space telescope to examine the conditions for the creation of planets. The researchers chose two stars outside our solar system, which analysis of the characteristics of the light coming from them indicates that they are quite young. The researchers wanted to observe the disk of dust around the stars, from which the planets are supposed to form. It is difficult to make such observations because the light coming from the disk is very weak compared to the dazzling light of the star. In order to distinguish the disk of dust surrounding the stars, the researchers used a camera sensitive to infrared radiation.
In this region, the light coming from the dust in the disk is relatively strong, while the light coming from the star is relatively weak. The sharpness of the images obtained from the space telescope makes it possible to hide the light of the star, so that the pale light emitted from the disk can be distinguished. The images obtained from the space telescope revealed details that had not been seen before: the researchers were able to clearly identify the dust disks around the two stars. It also became clear that the disks are not continuous: it is possible to notice that certain annular areas of the disks are free of dust.
The obvious explanation for this is that planets have already formed in these systems, which captured most of the dust and small particles of matter near their orbits. With the means of observation available to us today, it is impossible to see these planets themselves, because the light of their parent star reflected from them to us is too weak, but the trails they left behind in the gas disk, and the dust from which they were formed, testify to their existence.
